Apparatus for converting synthesis gas into higher hydrocarbons

ABSTRACT

Apparatus suitable for the conversion of synthesis gas to liquid hydrocarbon products, comprising a plurality of injector-mixing nozzles, a tank reactor, a gas recycle line having a first end and a second end and a slurry recycle line having a first end and a second end. The plurality of injector-mixing nozzles is arranged at or near the top of the tank reactor, each injector mixing nozzle having a first inlet for a suspension of a catalyst in a liquid medium, at least one second inlet for synthesis gas and an outlet positioned within the tank reactor for discharging a mixture of synthesis gas and the suspension from the injector-mixing nozzles in a downwards direction into the tank reactor. The tank reactor has a first outlet for discharging a product suspension at or near the bottom thereof and a second outlet for a gaseous recycle stream at or near the top thereof. The first end of the slurry recycle line is in communication with the first outlet of the tank reactor and the second end of the slurry recycle loop is in communication with the first inlet of the injector-mixing nozzles. The first end of the gas recycle line is in communication with the second outlet of the tank reactor and the second end of the gas recycle line is in communication with the second inlet(s) of the injector-mixing nozzles.

This application is a Divisional of application Ser. No. 10/155,359,filed May 28, 2002, the entire content of which is hereby incorporatedby reference in this application.

The present invention relates to a process for the conversion of carbonmonoxide and hydrogen (synthesis gas) to liquid hydrocarbon products inthe presence of a Fischer-Tropsch catalyst.

In the Fischer-Tropsch reaction a gaseous mixture of carbon monoxide andhydrogen is reacted in the presence of a heterogeneous catalyst to givea hydrocarbon mixture having a relatively broad molecular weightdistribution. This product is predominantly straight chain, saturatedhydrocarbons which typically have a chain length of more than 5 carbonatoms. The reaction is highly exothermic and therefore heat removal isone of the primary constraints of all Fischer-Tropsch processes. Thishas directed commercial processes away from fixed bed operation toslurry systems. Such slurry systems employ a suspension of catalystparticles in a liquid medium thereby allowing both the gross temperaturecontrol and the local temperature control (in the vicinity of individualcatalyst particles) to be significantly improved compared with fixed bedoperation.

Fischer-Tropsch processes are known which employ slurry bubble columnsin which the catalyst is primarily distributed and suspended in theslurry by the energy imparted from the synthesis gas rising from the gasdistribution means at the bottom of the slurry bubble column asdescribed in, for example, U.S. Pat. No. 5,252,613.

The Fischer-Tropsch process may also be operated by passing a stream ofthe liquid medium through a catalyst bed to support and disperse thecatalyst, as described in U.S. Pat. No. 5,776,988. In this approach thecatalyst is more uniformly dispersed throughout the liquid mediumallowing improvements in the operability and productivity of the processto be obtained.

However, there remains the need for further improvements in the mode ofoperation of a Fischer-Tropsch process.

The present invention relates to a process for the conversion of gaseousreactants to liquid hydrocarbon products by contacting the gaseousreactants at an elevated temperature and pressure with a suspensioncomprising catalyst suspended in a liquid medium, in a system comprisinga high shear mixing zone and a post mixing zone wherein the processcomprises:

a) passing the suspension comprising catalyst suspended in the liquidmedium through the high shear mixing zone where a gaseous reactantstream comprising the gaseous reactants is mixed with the suspension;

b) discharging a mixture comprising gaseous reactants and suspensionfrom the high shear mixing zone into the post mixing zone;

c) converting at least a portion of the gaseous reactants to liquidhydrocarbon products in the post mixing zone to form a productsuspension comprising catalyst suspended in the liquid medium and theliquid hydrocarbon products;

d) separating a gaseous stream comprising unconverted gaseous reactantsfrom the product suspension;

e) recycling the separated gaseous stream to the high shear mixing zone;and

f) recycling at least a portion of the product suspension to the highshear mixing zone.

An advantage of the process of the present invention over conventionalFischer-Trospch processes is that enhanced mass transfer in the highshear mixing zone and the post mixing zone improves the contact betweenthe gaseous reactants, liquid medium and solid catalyst and hencepromotes the catalytic conversion of the gaseous reactants to liquidhydrocarbon products. For avoidance of doubt, the conversion of thegaseous reactants to liquid hydrocarbon products is initiated in thehigh shear mixing zone although the majority of the conversion generallyoccurs in the post mixing zone.

Preferably, the gaseous reactants comprise a mixture of carbon monoxideand hydrogen (synthesis gas). Preferably, the ratio of hydrogen tocarbon monoxide in the synthesis gas is 2:1 by volume.

The synthesis gas may be prepared using any of the processes known inthe art including partial oxidation of hydrocarbons, steam reforming,and autothermal reforming. A discussion of these synthesis gasproduction technologies is provided in “Hydrocarbon Processing” V78,N.4, 87-90, 92-93 (April 1999) and “Petrole et Techniques”, N. 415,86-93 (July-August 1998). It is also envisaged that the synthesis gasmay be obtained by catalytic partial oxidation of hydrocarbons in amicrostructured reactor as exemplified in “IMRET 3: Proceedings of theThird International Conference on Microreaction Technology”, Editor WEhrfeld, Springer Verlag, 1999, pages 187-196. Alternatively, thesynthesis gas may be obtained by short contact time catalytic partialoxidation of hydrocarbonaceous feedstocks as described in EP 0303438.Preferably, the synthesis gas is obtained via a “Compact Reformer”process as described in “Hydrocarbon Engineering”, 2000, 5, (5), 67-69;“Hydrocarbon Processing”, 79/9, 34 (September 2000); “Today's Refinery”,15/8, 9 (August 2000); WO 99/02254; and WO 200023689.

Preferably, the liquid hydrocarbon products comprise a mixture ofhydrocarbons having a chain length of greater than 5 carbon atoms.Suitably, the liquid hydrocarbon products comprise a mixture ofhydrocarbons having chain lengths of from 5 to about 90 carbon atoms.Preferably, a major amount, for example, greater than 60% by weight, ofthe hydrocarbons have chain lengths of from 5 to 30 carbon atoms.

Suitably, the liquid medium comprises one or more of the liquidhydrocarbon products which has the advantage that there is norequirement to separate the liquid hydrocarbon products from the liquidmedium.

The high shear mixing zone may be part of the system inside or partiallyoutside the post mixing zone, for example, the high shear mixing zonemay project through the walls of the post mixing zone such that the highshear mixing zone discharges its contents into the post mixing zone. Thesystem may comprise a plurality of high shear mixing zones, preferablyup to 250 high shear mixing zones, more preferably less than 100, mostpreferably less than 50, for example 10 to 50 high shear mixing zones.Preferably, the plurality of high shear mixing zones discharge into asingle post mixing zone which has an advantage of significantly reducingthe size of a commercial Fischer-Tropsch plant. Preferably, theplurality of high shear mixing zones may be spaced uniformly inside orpartially outside the post mixing zone, for example, the high shearmixing zones may be spaced uniformly at or near the top of the postmixing zone. Preferably, the high shear mixing zones discharge themixture of gaseous reactants and suspension in a downwards directioninto the post mixing zone.

The high shear mixing zone(s) may comprise any device suitable forintensive mixing or dispersing of a gaseous stream in a suspension ofsolids in a liquid medium, for example, a rotor-stator device or aninjector-mixing nozzle.

The injector-mixing nozzle(s) can advantageously be executed as venturitubes (c.f. “Chemical Engineers' Handbook” by J. H. Perry, 3^(rd)edition (1953), p. 1285, FIG. 61), preferably an injector mixer (c.f.“Chemical Engineers' Handbook” by J H Perry, 3^(rd) edition (1953), p1203, FIG. 2 and “Chemical Engineers' Handbook” by R H Perry and C HChilton 5^(th) edition (1973) p 6-15, FIG. 16-31) or most preferably asa liquid-jet ejector,(c.f. “Unit Operations” by G G Brown et al, 4^(th)edition (1953), p. 194, FIG. 210). Alternatively, the injector-mixingnozzle(s) may be executed as “gas blast” or “gas assist” nozzles wheregas expansion is used to drive the nozzle (c.f. “Atomisation and Sprays”by Arthur H Lefebvre, Hemisphere Publishing Corporation, 1989). Wherethe injector-mixing nozzle(s) is executed as a “gas blast” or “gasassist” nozzle, the suspension of catalyst is fed to the nozzle at asufficiently high pressure to allow the suspension to pass through thenozzle while the gaseous reactant stream is fed to the nozzle at asufficiently high pressure to achieve high shear mixing within thenozzle.

Suitably, the gaseous reactant stream is fed to the high shear mixingzone at a pressure of at least 20 bar, preferably at least 30 bar.Typically, the pressure drop of the suspension over the high shearmixing zone is in the range of from 1 to 6 bar, preferably 2 to 5 bar,more preferably 3 to 4 bar. An advantage of the process of the presentinvention is that where the gaseous reactant stream comprises synthesisgas obtained via a “Compact Reformer” process, the synthesis gas isgenerally at a pressure of above 20 bar. Accordingly, there is norequirement to lower the pressure of the synthesis gas before feedingthe synthesis gas to the process of the present invention therebyproviding an energy efficient integrated Reforming/Fischer Tropschprocess. In particular, the pressure of synthesis gas obtained via a“Compact Reformer” process is generally sufficiently high to achievehigh shear mixing within a “gas blast” or “gas assist” nozzle.

Suitably, the shear forces exerted on the suspension in the high shearmixing zone(s) are sufficiently high that the gaseous reactant stream isbroken down into gas bubbles having diameters in the range of from 30μto 10 mm, preferably from 30 g to 3000μ, more preferably from 30μ to300μ.

Preferably, the product suspension which is recycled to the high shearmixing zone (hereinafter referred to as “suspension recycle stream”) iscooled outside of the high shear mixing zone and the post mixing zone,in order to assist in the removal of exothermic heat of reaction fromthe system, for example, by passing the suspension recycle streamthrough a heat exchanger. Preferably, the suspension recycle stream iscooled to a temperature of not more than 12° C. below the temperature ofthe suspension in the post mixing zone.

Preferably, additional cooling is provided within the post mixing zoneby means of a heat exchanger, for example, heat transfer tubes,positioned within the suspension in the post mixing zone.

The gaseous stream comprising unconverted gaseous reactants may beseparated from the product suspension either within the post mixing zoneor in an external gas liquid separation zone. The separated gaseousstream may comprise vaporized low boiling liquid hydrocarbon products,vaporized water by-product and gaseous hydrocarbons having from 1 to 3carbon atoms such as methane, ethane and propane, in addition tounconverted gaseous reactants.

The separated gaseous stream (hereinafter referred to as “gaseousrecycle stream”) may be cooled before being recycled to the high shearmixing zone, for example, by passing the gaseous recycle stream througha heat exchanger, to assist in the removal of the exothermic heat ofreaction from the system. Where the gaseous recycle stream is cooled tobelow its dew point, any vaporized low boiling liquid hydrocarbonproducts and any vaporized water by-product will condense out of thegaseous recycle stream and these condensed liquids are preferablyremoved from the system using a suitable separation means, for example,the heat exchanger may be fitted with a liquid trap. Water by-productmay then be separated from the condensed low boiling liquid hydrocarbonproducts using a suitable separation means, such as a decanter. The lowboiling hydrocarbon products may then be recycled to the high shearmixing zone and/or the post mixing zone. Fresh gaseous reactants may befed to the gaseous recycle stream, either upstream or downstream of theheat exchanger. Where the fresh gaseous reactants have not beenpre-cooled, it is preferred that the fresh gaseous reactants are fed tothe gaseous recycle stream upstream of the heat exchanger.

Preferably, the gaseous stream which is recycled to the high shearmixing zone comprises from 5 to 50% by volume of fresh gaseousreactants.

Preferably, a purge stream is taken from the gaseous recycle stream toprevent accumulation of gaseous by-products, for example, methane, inthe system. If desired, any gaseous intermediate products (gaseoushydrocarbons having 2 or 3 carbon atoms) may be separated from the purgestream. Preferably, such gaseous intermediate products are recycled tothe system where they may be converted to liquid hydrocarbon products.

Preferably, a stream comprising low boiling hydrocarbon(s) (for examplepentanes, hexanes or hexenes) may be introduced into the high shearmixing zone and/or the post mixing zone. Without wishing to be bound byany theory, it is believed that vaporisation of the low boilinghydrocarbon(s) (hereinafter referred to as “low boiling solvent”) in thehigh shear mixing zone and/or the post mixing zone aids and enhances themixing of the gaseous reactants, liquid medium and the solid catalystthereby increasing conversion of the gaseous reactants to liquidhydrocarbon products. Moreover, vaporisation of the low boiling solventwill also assist in removing some of the exothermic heat of reactionthereby allowing more control over the product selectivities andminimising the production of gaseous by-products, for example, methane.For avoidance of doubt, it is envisaged that the low boiling solvent mayvaporise in both the post mixing zone and the high shear mixing zone.The gaseous recycle stream may therefore comprise vaporized low boilingsolvent in addition to vaporized low boiling liquid hydrocarbonproducts, vaporized water by-product, unconverted gaseous reactants andgaseous hydrocarbons having from 1 to 3 carbon atoms. As discussedabove, the gaseous recycle stream may be cooled before being recycled tothe high shear mixing zone. Any vaporized low boiling solvent maycondense, together with any vaporized low boiling liquid hydrocarbonproducts and any vaporized water by-product, upon cooling the gaseousrecycle stream to below its dew point. Preferably, the condensed liquidsare removed from the system, as described above, and water by-productmay then be separated from the condensed liquids using a suitableseparation means, also as described above. The remaining condensedliquids may then be recycled to the high shear mixing zone and/or thepost mixing zone.

For practical reasons the post mixing zone may not be totally filledwith suspension during the process of the present invention so thatabove a certain level of suspension a gas cap containing unconvertedgaseous reactants is present in the top of post mixing zone. Suitably,the volume of the gas cap is not more than 40%, preferably not more than30% of the volume of the post mixing zone. The high shear mixing zonemay discharge into the post mixing zone either above or below the levelof suspension in the post mixing zone. An advantage of the high shearmixing zone discharging below the level of suspension is that thisimproves the contact between the gaseous reactants and the suspension inthe post mixing zone.

Where the post mixing zone has a gas cap, the gaseous recycle stream maybe withdrawn from the gas cap. It is also envisaged that the post mixingzone may be fitted with an overhead condenser or cooler for removal ofheat from the gases in the gas cap. Where the post mixing zone is fittedwith an overhead condenser or cooler, the gaseous recycle stream may bewithdrawn from the overhead condenser or cooler (i.e. is withdrawnindirectly from the post mixing zone). Any low boiling liquidhydrocarbon products and low boiling solvent which condense in thecondenser or cooler may be collected and recycled to the high shearmixing zone or the post mixing zone (after having separated any waterby-product).

The catalyst which may be employed in the process of the presentinvention is any catalyst known to be active in Fischer-Tropschsynthesis. For example, Group VIII metals whether supported orunsupported are known Fischer-Tropsch catalysts. Of these iron, cobaltand ruthenium are preferred, particularly iron and cobalt, mostparticularly cobalt.

A preferred catalyst is supported on an inorganic refractory oxide.Preferred supports include silica, alumina, silica-alumina, the GroupIVB: oxides, titania (primarily in the rutile form) and most preferablyzinc oxide. The supports generally have a surface area of less thanabout 100 m²/g, preferably less than 50 m²/g, more preferably less than25 m²/g, for example, about 5 m²/g.

The catalytic metal is present in catalytically active amounts usuallyabout 1-100 wt %, the upper limit being attained in the case of ironbased catalysts, preferably 2-40 wt %. Promoters may be added to thecatalyst and are well known in the Fischer-Trospch catalyst art.Promoters can include ruthenium, platinum or palladium (when not theprimary catalyst metal), rhenium, hafnium, cerium, lanthanum andzirconium, and are usually present in amounts less than the primarycatalytic metal (except for ruthenium which may be present in coequalamounts), but the promoter:metal ratio should be at least 1:10.Preferred promoters are rhenium and hafnium.

A further advantage of the process of the present invention is thatintensive mixing of the gaseous reactant stream and the suspension ofcatalyst in the high shear mixing zone allows smaller catalyst particlesizes to be employed compared with a conventional slurry process. Thus,the catalyst may have a particle size of less than 50 microns,preferably less than 40 microns, for example, in the range 5 to 30microns. In contrast, a conventional slurry process will typicallyemploy a catalyst having a particle size of greater than 40 microns.Advantages of smaller catalyst particle sizes include reducing theselectivity of the process of the present invention to methane (agaseous by-product) and also reducing the formation of heavierhydrocarbon products. Without wishing to be bound by any theory, it isbelieved that catalyst particles having the preferred particle size ofless than 40 microns may be formed in situ in the system by attrition oflarger sized catalyst particles, for example, by attrition of a catalysthaving a particle size of greater than 50 microns.

Preferably, the suspension of catalyst discharged into the post mixingzone comprises less than 40% wt of catalyst particles, more preferably10 to 30% wt of catalyst particles, most preferably 10 to 20% wt ofcatalyst particles.

In a preferred embodiment the process is carried out using aninjector-mixing nozzle. It has been found that intensive mixing of thegaseous reactant stream, the liquid medium and the solid catalyst can beachieved in the injector-mixing nozzle leading to high conversions ofgaseous reactants to liquid hydrocarbon products in the post mixingzone. The suspension which is discharged by the injector-mixing nozzleinto the post mixing zone is at least in part recycled to theinjector-mixing nozzle, for example, via a slurry pump. Theinjector-mixing nozzle may draw in the gaseous reactant stream throughat least one opening in its side wall (a venturi nozzle). Alternatively,as described above, the gaseous reactant stream may be supplied at highpressure to the injector-mixing nozzle through at least one opening inits side wall (a “gas blast” or “gas assist” nozzle). An advantage ofusing a “gas blast” or “gas assist” nozzle as the high shear mixing zoneis that there is a reduced duty on the slurry pump.

More than one injector-mixing nozzle, preferably up to 150, morepreferably less than 100, most preferably less than 50, for example 10to 50 injector-mixing nozzles may discharge into a single post mixingzone.

Suitably, the post mixing zone comprises a vessel, for example, a tankreactor or a tubular loop conduit and the injector-mixing nozzle can beplaced at any position on the walls of the vessel (for example, at thetop, bottom or side walls of a tank reactor).

Where the vessel of the post mixing zone is a tank reactor, productsuspension is withdrawn from the tank reactor and is at least in partrecycled to the injector-mixing nozzle(s). Very good mixing can beachieved when the injector-mixing nozzle(s) is situated at the top ofthe tank reactor and the suspension is removed from the tank reactor atits bottom. Therefore the tank reactor is preferably provided at its topwith at least one injector-mixing nozzle and the suspension recyclestream is preferably withdrawn from the bottom of the tank reactor.Preferably, the suspension recycle stream is at least in part recycledvia a loop conduit (slurry recycle line) to the top of theinjector-mixing nozzle(s) through which it is then injected into the topof the tank reactor, the gaseous reactant stream being introducedthrough one or more openings in the side wall of the injector-mixingnozzle(s). Preferably, a heat-exchanger is positioned on the loopconduit to remove the heat of reaction.

Where the vessel of the post mixing zone is a tubular loop conduit, asingle injector-mixing nozzle may discharge into the tubular loopconduit. Suspension may be recycled to the injector-mixing nozzle, forexample, via a pump or propeller positioned in the tubular loop conduit.A heat exchanger may be disposed along at least part of the length ofthe tubular loop conduit, preferably along substantially the entirelength of the tubular loop conduit thereby providing temperaturecontrol. Alternatively, a series of injector-mixing nozzles may bearranged around the tubular loop conduit. In this arrangement eachinjector-mixing nozzle discharges into a section of the tubular loopconduit which section recycles the suspension to the nextinjector-mixing nozzle in the loop, for example, via a pump or propellerpositioned in the section of the tubular loop conduit. A heat exchangermay be disposed along at least part of each section of tubular loopconduit, preferably along substantially the entire length of eachsection of tubular loop conduit thereby providing temperature control.It is envisaged that mixing of the gaseous reactants and the suspensionof catalyst in the tubular loop conduit may be so efficient that thereis no requirement for a gas cap. Where a gas cap is omitted, productsuspension together with entrained and/or dissolved gases (unconvertedgaseous reactants, gaseous hydrocarbons having from 1 to 3 carbon atoms,vaporized low boiling liquid hydrocarbon products, vaporized waterby-product and optionally vaporized low boiling solvent) is withdrawnfrom the tubular loop conduit and a gaseous recycle stream comprisingthe entrained and/or dissolved gases is separated from the productsuspension in an external gas liquid separation zone.

Where the vessel of the post mixing zone (e.g. tank reactor or tubularloop conduit) has a gas cap, advantageously the gaseous recycle streamis withdrawn through the vessel wall from the gas cap and is recycled tothe injector-mixing nozzle(s). As mentioned above, an advantage ofrecycling the gaseous reactants from the gas cap to the injector-mixingnozzle(s) is that in this manner the temperature of the suspension inthe vessel can be advantageously controlled by cooling the gaseousrecycle stream in a heat exchanger outside the high shear mixing zoneand the vessel of the post mixing zone. This temperature control can befurther improved if fresh gaseous reactants are added to the gaseousrecycle stream before it is cooled (upstream of the heat exchanger) orare pre-cooled. The temperature of the suspension in a tank reactor canalso be controlled by means of a heat exchanger, for example, heattransfer tubes, positioned below the level of suspension in the tankreactor and by means of external cooling of the suspension recyclestream.

The process of the invention is preferably carried out at a temperatureof 180-280° C., more preferably 190-240° C.

The process of the invention is preferably carried out at a pressure of5-50 bar, more preferably 15-35 bar, generally 20-30 bar.

The process of the present invention can be operated in batch orcontinuous mode, the latter being preferred.

In a continuous process part of the product suspension is continuouslyremoved from the system and is passed to a suitable separation means,where liquid medium and liquid hydrocarbon products are separated fromthe catalyst. Examples of suitable separation means includehydrocyclones, filters, gravity separators and magnetic separators.Alternatively, the liquid medium and liquid hydrocarbon products may beseparated from the catalyst by distillation. The separated liquids arethen passed to a product purification stage where water by-product andliquid medium are removed from the liquid hydrocarbon products. Asdiscussed above, the purification stage may be simplified by using oneor more of the liquid hydrocarbon products as the liquid medium in whichcase there is no requirement to separate the liquid medium from theliquid hydrocarbon products. The catalyst may be recycled as aconcentrated slurry to the post mixing zone. Fresh catalyst may be addedeither to the recycled slurry or directly into the post mixing zone.

In order to prevent the accumulation of water by-product in the systemit is preferred that at least a portion of the water by-product isremoved from the suspension recycle stream, This may be achieved bytaking a side stream from the suspension recycle stream downstream ofthe heat exchanger. The liquid components of the side stream areseparated from the catalyst (as described above) and water by-product isremoved from the separated liquids (also as described above) beforerecycling the remaining separated liquid components back to the highshear mixing zone. The separated catalyst may be recycled to the postmixing zone as a concentrated slurry (as described above).

It is envisaged that removal of water by-product from the system can beincorporated into the product separation stage, by recycling a portionof the separated liquids, from which water has been removed, back to thehigh shear mixing zone.

The liquid hydrocarbon products from the purification stage may be fedto a hydrocracking stage, for example, a catalytic hydrocracking stagewhich employs a catalyst comprising a metal selected from the groupconsisting of cobalt, molybdenum, nickel and tungsten supported on asupport material such as alumina, silica-alumina or a zeolite.Preferably, the catalyst comprises cobalt/molybdenum ornickel/molybdenum supported on alumina or silica-alumina. Suitablehydrocracking catalysts include catalysts supplied by Akzo Nobel,Criterion, Chevron, or UOP. A preferred catalyst is KF 1022™, acobalt/molybdenum on alumina catalyst, supplied by Akzo Nobel.

BRIEF DESCRIPTION OF DRAWINGS

The invention will now be illustrated with the aid of a Figure.

A suspension of a catalyst in a liquid medium is recycled to aninjector-mixing nozzle (1) via a line (2). Through one or more openingsin the side wall of the injector-mixing nozzle (1) the suspension drawsin a gaseous reactant stream comprising carbon monoxide and hydrogen,which is introduced into the injector-mixing nozzle (1) via a line (3).Fresh gaseous reactants are introduced via a line (4) into the line (3)through which unconverted gaseous reactants are recycled from a gas cap(5) which is present in the upper part of a vessel (6) the lower part ofwhich contains a suspension (7) of the catalyst in a mixture of theliquid medium and liquid hydrocarbon products. A dotted line (8) in theFigure denotes the upper level of the suspension (7) in the vessel (6).

By means of cooling in a heat exchanger (9) the gas mixture passingthrough the line (3) is maintained at the correct operating temperature.Suitably, the heat exchanger (9) is a condenser having a water trap forremoving water by-product from the system. A purge stream (10) is takenfrom the line (3) to prevent the build up of gaseous by-products in thegas cap (5). Optionally, a heat exchanger (11) e.g. cooling tubes isprovided below the level of the suspension (7) in the vessel (6) toassist in removing the exothermic heat of reaction.

Optionally, a stream of low boiling hydrocarbon liquid(s) (low boilingsolvent) may be introduced to the injector-mixing nozzle (1) via line(12) or alternatively to the vessel (6), via line (13). Where lowboiling hydrocarbon liquid(s) are introduced to the system these maycondense in the heat exchanger (9). The condensed low boilinghydrocarbon liquid(s) may be separated from the condensed waterby-product in a decanter (not shown). The separated low boilinghydrocarbon liquid(s) may then be recycled to the system.

Via a lower outlet opening of the injector-mixing nozzle (1) the mixtureof catalyst, liquid medium, liquid hydrocarbon products and unconvertedgaseous reactants pass into the vessel (6) below the level (8) of thesuspension (7). The unconverted gaseous reactants then separate into thegas cap (5).

Via a line (14) the suspension (7) is withdrawn from the bottom of thevessel (6) and at least a portion of the suspension is recycled to theinjector-mixing nozzle (1) by means of pump (15) and the line (2). Bymeans of cooling in a heat exchanger (16) the recycled suspension in theline (2) is maintained at the correct operating temperature.

Via a line (17) a portion of the suspension (7) is withdrawn from thesystem. By a suitable separation means (18), e.g. a hydrocyclone,filter, gravity separator or magnetic separator, or alternatively, bydistillation, the liquid medium and liquid hydrocarbon products may beseparated from the suspended catalyst. Separated catalyst may bereturned to the vessel (6) as a slurry via a slurry pump (19) and a line(20). The separated liquid medium and liquid hydrocarbon products may bepassed from the separation means (18) to a purification zone (notshown).

A portion of suspension may be withdrawn from line (2) and may be passedalong line (21) to a separation means (22) where the liquid componentsof the suspension are separated from the catalyst (e.g., as describedabove). The separated liquids are then passed along line (23) to adecanter (24) where water by-product is removed from the system via line(25). The remaining liquids are then reintroduced into line (2) via line(26). The separated catalyst, from decanter (24), is introduced as aslurry into line (20) via a line (27).

We claim:
 1. An apparatus suitable for the conversion of synthesis gasto liquid hydrocarbon products, which comprises a plurality ofinjector-mixing nozzles, a tank reactor, a gas recycle line having afirst end and a second end and a slurry recycle line having a first endand a second end wherein: a) the plurality of injector-mixing nozzlesare arranged at or near the top of the tank reactor; b) each injectormixing nozzle has a first inlet for a suspension of a catalyst in aliquid medium, at least one second inlet for synthesis gas and an outletwhich is positioned within the tank reactor for discharging a mixture ofsynthesis gas and the suspension from the injector-mixing nozzles in adownwards direction into the tank reactor, c) the tank reactor has afirst outlet for discharging a product suspension at or near the bottomthereof and a second outlet for a gaseous recycle stream at or near thetop thereof; d) the first end of the slurry recycle line is incommunication with the first outlet of the tank reactor and the secondend of the slurry recycle loop is in communication with the first inletof the injector-mixing nozzles; and e) the first end of the gas recycleline is in communication with the second outlet of the tank reactor andthe second end of the gas recycle line is in communication with thesecond inlet(s) of the injector-mixing nozzles.
 2. An apparatus asclaimed in claim 1 wherein the slurry recycle line is provided with aslurry pump and a heat exchanger.
 3. An apparatus as claimed in claim 1wherein the gas recycle line is provided with a heat exchanger.
 4. Anapparatus as claimed in claim 1 wherein the apparatus has up to 150injector-mixing nozzles.
 5. An apparatus as claimed in claim 1 whereinthe tank reactor has a heat exchanger positioned therein.